Scientists within the MedSeA project have been examining the concentration of human-produced carbon, taken from Mediterranean field measurements, which is high and unusually penetrating deeper waters. Typically ocean acidification (pH decrease) affects the sea surface but this work has identified evidence of pH decrease throughout the water column, with the effect being more prominent in the NW Mediterranean Sea. Due to the complexity and high variability of the Mediterranean basin, ocean acidification will have different regional impacts, such as in regions where projections of (winter and summer) sea surface temperature are likely to increase up to 2oC by the year 2050, if rates of anthropogenic CO2 emissions continue at today’s rate.

Today carbon dioxide is increasing in the atmosphere faster than land and oceans can absorb it, and the average acidity of the oceans has increased . Two ongoing European projects on Ocean Acidification EPOCA (European project on ocean acidification) and MedSeA (The European Mediterranean Sea Acidification in a changing climate) consider these issues forEuropes. Jean-Pierre Gattuso, research scientist at the Laboratoire d’océanographie de Villefranche (CNRS/UPMC) is EPOCA’s co-ordinator and a member of the scientific steering committeee of MedSeA. In a recent interview, he discusses ocean acidification for all of Europe’s seas and oceans, whether the Arctic Ocean, the Atlantic Ocean or theMediterranean Sea. Highlights and research efforts for theMediterranean Seaare provided below:

Ocean acidification is a very recent science, so difficult to predict the future of the southern Atlantic Ocean and Mediterranean Seain high CO2 conditions. In the Mediterranean, Posidonia oceanica, which is using CO2 for photosynthesis, so when it has more CO2 it grows faster and it benefits from higher CO2 levels, in contrast with most of the other algae and plants which use bicarbonate.The main negative aspect is for calcifiers. As ocean acidification proceeds, carbonate becomes less abundant, so carbonate concentration in water limits the precipitation of calcium carbonate, and organisms have a harder time to make their shells and skeletons. In parallel, water becomes more corrosive, with greater damage to shells and skeleton. Some organisms are becoming fragile as they dissolve faster than their shell is built. There is a clear need for research on these biogeochemical impacts, and EU is leading through the work of EPOCA and MedSeA.

Ocean acidification is progressing faster in colder water because gas is more soluble in cold water and dissolves faster. As CO2 increases in the atmosphere and goes into the water, the corrosiveness of water or the impact of the increasing acidity appears first in the polar oceans and later in temperate and tropical seas such as theMediterranean Sea. TheArcticis a hot spot for ocean acidification as it is for global warming and sea ice melting. EPOCA has done a lot of work in the Arctic both in terms of chemistry and of biological response. Biologically, even if ocean acidification progresses slower in temperate and tropical waters, the combination of ocean acidification and warm temperature is a bad recipe for Mediterranean coral reefs. In EPOCA, ocean acidification work is occurring along the coasts ofFrance,SpainandPortugal, and the Canary current close to the Canary islands, with comparitive work in the Gulf of California, the PacificOcean andFiji. Within MedSeA, other research is conducted. For example, in Corsica andCrete, a mesocosm experiments are conducted where impacts of different CO2 levels on large enclosures water and marine organisms over 6 to 8 week periods. The Institut de Ciencies del Mar, CSIC,Barcelona, is measuring the response of commercial mollusks to ocean acidification levels in the sea and in lab conditions. MedSeA translates research obtained in the lab and the sea, with socio-economic partners translating biological and biogeochemical information into socio-economic impacts.